Essential Oil Composition of Sideritis pusilla (Lange) Pau ssp.
The quantitative composition of the essential oils from several subspecies, varieties and populations of Sideritis pusilla (Lange) Pau (Lamiaceae), analyzed by GC and GC/MS, is reported. Monoterpene hydrocarbons, alcohols, sesquiterpenes and diterpenes were the main constituents in all samples. Among these, α-pinene (7.1-25.4%), sabinene (5.9-20.4%), fenchone (0.9-19.3%), limonene (1.2-7.4%) and 1,8-cineole (1.8-15.6%) were the major compounds. The results confirm that there are differences between varieties and subspecies, while cluster analysis revealed that the oil composition potentially has chemotaxonomical significance for this taxon.
Key Word Index
Sideritis pusilla ssp. oxteoxylla, Sideritis pusilla ssp. almeriensis, Sideritis pusilla ssp. pusilla, Sideritis pusilla ssp. flavovirens, Lamiaceae, chemotaxonomy, essential oil composition, α-pinene, sabinene, fenchone, 1,8-cineole.
The genus Sideritis L. (Lamiaceae) is highly widespread in the Mediterranean area, comprising more than 100 species. Among them, more than 18 grow in the Iberian Peninsula, and most of these species are endemic. The great botanical interest in Sideritis species (1) is due to the strong tendency of some to hybridize, which makes it difficult to classify them. While the dried inflorescences of some Sideritis species are used in eastern Mediterranean countries to prepare herbal teas, which are considered to have medicinal properties, some other therapeutic applications have been described. Thus, infusions of the aerial parts of these species are used as tonics, carminatives, as anti-inflammatory agents, antispasmodics, diuretics and digestives, and in the treatment of colds (2,3).
The oils of several Iberian species of the genus Sideritis have been studied, like S. funkiana (4), S. hirsute, (5), S. javalambrensis (6), S. tragoriganum (7) and S. mugronensis (8), containing hydrocarbons as their main reported constituents. Although the S. pusilla oil composition has been reported (9), so far no studies at the infraspecific level have been accomplished for this taxon.
As a part of a study of the chemical composition of endemic plants of southeastern Spain, we report the qualitative and quantitative analysis of the oils of eight infraspecific taxa of S. pusilla.
Previous to the samples taxa selection, a genetic study was carried out into infraspecific taxa of S. pusilla, in order to elucidate a relationship and population structure within taxa (10), which agree with the classifications made by Pallarés (1).
Although several studies on the hexane extracts of S. pusilla have shown the presence of diterpenic components in the plant (11-14), there are no reports on the composition of the oil at the infraspecific taxa for this species.
The aerial parts (~35 cm) of each taxa growing wild in eight localities of Almería province (Table I) were collected in May 1996.
Voucher specimens of each subspecies have been deposited in the Herbarium of the University of Almería (ALMEU658-672), and are available for inspection on request. All samples were collected at full flowering. The ratio of stems/leaves/flowers is approximately the same in all samples. The plants were dried at room temperature (20°-25°C). The oils were prepared by steam distillation of 100-200 g of air-dried plants for 6 h. Yields ranged from 1.5% to 2.0%.
The analyses of the oils were carried out by GC and GC/ MS. The HP 5890II gas Chromatograph equipped with FID and methylsilicone HP-5MS (crosslinked 5% PH ME Siloxane) capillary column (30 m × 0.25 mm), film thickness 0.25 µm, was used for quantitative analysis. The GC oven temperature was varied from 50°-250°C at a rate of 3°C/min, using He as the carrier gas (1.5 mL/min). Injector and detector temperatures were 250°C and 300°C respectively. Analyses by GC/MS were performed, using an HP 5890II Chromatograph interfaced to an HP 5972 mass spectrometer (ionization voltage 70 eV) and equipped with capillary column HP-5MS (crosslinked 5% PH ME Siloxane) capillary column (30 m × 0.25 mm), film thickness 0.25 µm. The oven temperature was programmed from 50° 250°C at a rate of 3°C/min, using He as the carrier gas (1.5 mL/ min). Injector and detector temperatures were 250°C and 300°C, respectively.
The percentage composition of the oils was computed from GC peak areas without correction factors. Qualitative analyses were based on a comparison of retention indices and mass spectra with corresponding data in the literature (15) and computer mass spectra libraries (Wiley and NBS 54K).
Statistical analysis: Cluster analyses were performed with the software package Statgraphics for Windows v. 4.1.
Results and Discussion
The nomenclature proposed by Pallares (1) has been used in this study. This author distinguished four subspecies, two with three varieties, which accounts for a total of eight taxa within S. pusilla. All were collected and studied. The exact locations in UTM coordinates are shown in Table I.
Table II shows the qualitative and quantitative composition of the oils. The plants S. pusilla ssp. oxteoxylla (entry OST) and S, pusilla ssp. flaOovirens (entry FLA) were collected from several locations, but showed no significant morphological differences, and only a representative sample was analyzed for each one. Three varieties of the subspecies almeriensis were considered for the study, which were classified as S. pusilla ssp. almeriensis var. typica (entry ALM), S. pusilla ssp. almeriensis var. littoralis (entry LIT) and S. pusilla ssp. almeriensis var. salina (entry SAL). Another three varieties of the subspecies pusilla were considered for the study: S. pusilla ssp. pusilla var. typica (entry PUS), S. pusilla ssp. pusilla var. carthaginensis (entry CAR) and S. pusilla ssp. pusilla var. granatensis. Strong morphological differences were found for two populations of the latter one, growing in the same area. Both were collected and analyzed, but no significant differences were found in the chemical composition, and only a representative result is shown in Table II (entry GRA).
Forty-eight different compounds in total were identified. Monoterpene hydrocarbons were the main group of constituents in all samples, but alcohols, sesquiterpenes and diterpenes were also present. α-Pinene and sabinene were, in general, the main constituents.
The popular uses of S. pusilla is supported by the described composition. Thus, the presence in the oil of fenchone and limonene, which are used as flavoring agents, justifies its use as an aromatic tea. Other uses are related to the presence of α-pinene and limonene, which are described as antibacterial, antiviral, anti-inflammatory and anti-cancer agents. In addition, it is reported that α-pinene has spasmogenic and tranquilizer properties (16).
Two samples, S. pusilla ssp. almeriensis var. salina (entry SAL) and S. pusilla subsp. pusilla var. carthaginensis (entry CAR) contain a peak, which on the basis of its mass spectrum is considered to be 15 beyerene, previously found in the hexane extracts of S. pusilla (14).
The results show some qualitative and quantitative differences between the components of the oils. These results were expected as the composition of the essential oils from Sideritis species is largely influenced by the season, geographical location, plant variety and data of collection (9). Nevertheless, at the infraspecific level here considered, the essential components of the oil potentially have taxonomical value. This way, by using the main compounds found in the oil (> 1% for all species), a cluster analysis has been affected. The dendrogram (Nearest Neighbor Method, Squared Euclidean) (Figure 1) shows a complete correlation among taxonomical classification ( 1 ) and genetic analysis (10). Thus, the oil profile might be considered as a taxonomical marker for this species; however, more populations need to be examined before this concept is fully accepted.
As is mentioned above, the oil composition for S. pusilla has been reported previously (9). Nevertheless, the authors did not specify any infra-specific taxon for this species in the two different populations analyzed. Looking at the locations where these species were collected, as well as the oil composition reported, we believe that the the complete taxon for S. pusilla samples collected in Adra by these authors is S. pusilla ssp. almeriensis, while the species gathered in Nijar would be assimilated to a S. pusilla ssp. pusilla var. carthaginensis.
The results confirm that there are differences between populations within the same subspecies, and some compounds that justify their use in traditional medicine.
The authors wish to thank the Instituto de Estudios Almerienses for financial support.
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Ignacio Rodríguez-García and Manuel Muñoz-Dorado
Dpt. Química Orgánica, Universidad de Almería, 04120 Almería, Spain
Dpt. Biología Vegetal y Ecología, Universidad de Almería, 04120 Almería, Spain
Dpt. Bioquímica, Universidad de Almería, 04120 Almería, Spain
Dpt. Ingeniería Química, Universidad de Almería, 04120 Almería, Spain
* Address for correspondence
10410 -2905/04/00060 -0535$6.00/0-© 2004 Allured Publishing Corp.
Received: September 2002
Revised: November 2002
Accepted: January 2003
Copyright Allured Publishing Corporation Nov/Dec 2004
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